In recent years, CATV operators have transformed their services from providing standard cable television entertainment content to providing television, voice, security, and broadband services, all through a single cable. As a result, modern communications infrastructures have had to meet rising demand by providing much larger amounts of bandwidth as both the number of subscribers have increased and the services those subscribers use have increasingly consumed more bandwidth. For instance, bandwidth-intensive internet applications such as file sharing, video conferencing, e-commerce, and audio and video consumption have become incredibly popular. To address this rising demand, some incumbent local exchange carriers and competitive local exchange carriers have completely replaced their networks with fiber-based technologies capable of carrying more data than conventional coaxial cable systems. However, infrastructure modifications are costly in both time and expense, and are therefore not an attractive solution to some carriers.
Some operators have attempted to satisfy the ever-increasing demand for bandwidth in other ways. For example, some operators have implemented higher modulation schemes for both forward path (“downstream”) signals and return path (“upstream”) signals. Currently, many CATV operators use 256 quadrature amplitude modulation (“QAM”) for downstream or forward path signals, and are actively migrating from 16 QAM to 64 QAM for upstream or return path signals. Several return path signals from a single house are typically combined into a single upstream signal, which is then combined with many other similar signals from other homes, so that a combined upstream signal is transmitted to back to the operator.
Hybrid fiber-coaxial (“HFC”) systems provide this bi-directional data transmission, with return path signals being transmitted to an HFC plant to provide information about the system, such as the operability, status, load, or use of the system and by the consumer. HFC networks transmit data using the cable service interface specification (“DOCSIS”) standard for bi-directional data transmission. DOCSIS devices such as cable modems, embedded multimedia terminal adapters (“EMTAs”), and cable set-top boxes in a subscriber's home transmit return path data in periodic bursts. When the electronic device is not actively transmitting data, it is inactive. However, while the device is inactive and not transmitting a signal, noise, known as ingress noise, is still transmitted along the line from construction or installation imperfections in the electronic devices and cables, poor shielding in the devices and cables, distortions in devices and cables, and other sources. Further, as higher levels of modulation are used, the required signal to noise ratio (“SNR”) increases. This means that the “good,” or valid, signals originating from devices like cable modems, EMTAs, and cable set-top boxes must be at a sufficient power level above interfering noise to ensure good data transmission quality. Furthermore, the HFC network must provide a guaranteed level of service to ensure the quality of voice communications and to accommodate VoIP (Voice over Internet Protocol).
As a consequence of combining return path signals for transmission back to an HFC plant, return path ingress noise is combined and transmitted to the HFC plant. When ingress noise is combined from among many houses, a noise funneling effect is created which negatively impacts the SNR of the system and effectively sets the limit on the number of homes per node, as well as the highest modulation level that can be used. Conventional attempts by CATV operators to reduce ingress noise so that higher modulation levels can be used include reducing node sizes, which requires expensive HFC plant upgrades consisting of new optical fiber installation and capital equipment investment.
The VoIP services provided by CATV operators are of particular importance, because VoIP is used to provide telephone communications, which are critical or essential services in crises such as natural disasters or emergencies. While these services must be operational during crises, they typically rely on powered equipment and powered signals. That power can be disrupted or discontinued during crises. If an emergency or disaster results in the loss of power, the VoIP services will typically lost as well. An improved amplifier is needed.